Crank counterbalance



NOV. 18, 1952 5 s, SHQUP 2,618,172

CRANK COUNTERBALANCE Filed Aug. 17, 1950 3 Sheets-Sheet I5 INVENTOR. 5 +80 /e S- 5A a (JP A TTOENE-Y Patented Nov. 18, 1952 CRANK COUNTERBALANCE Stanley S. Shoup, Toledo, Ohio, assignor to The National Supply Company, Pittsburgh, Pa., a corporation of Pennsylvania Application August 17, 1950, Serial No. 180,039

2 Claims. 1

This invention relates generally to counterbalancing devices for crankshafts of oil well pumping apparatus and more particularly to improvements in the construction and the manner of attaching and securing the counterbalancing weights to a rotating crank.

The principal object of this invention is to provide a unitary counterbalancing crank weight and improved means for securing the same to a rotatable crank member for use with oil well pumping apparatus. Another object of this invention is to provide a unitary counterbalancing crank weight which will freely slide around a circular T-section rim of a crank while in its unclamped position on the rim and yet adapted to be firmly clamped and secured at a selected position on said rim such that it will not move relative thereto under the severest operating conditions.

Another object of this invention is to provide a one piece counterbalancing crank weight that is adapted to hang plumb on the T-section rim of a crank when the weight is loose on the crank and to remain plumb after the weight is tightly secured to said rim.

Another object of this invention is to provide a one piece counterbalancing crank weight that is capable of being securely tightened on the T- section rim of a crank without putting any clamping strain on the lips of the counterbalancing crank weight.

Another object of this invention is to provide a one piece counterbalancing crank weight that is capable of being securely tightened on the T-section rim of a crank in a manner that 1 the clamping action is such that the frictional resistance of the surfaces in contact will over-' come all static and dynamic forces tending to throw the weight ofi the crank.

Another object of this invention is to provide a unitary counterbalancing crank weight that is easily adjustable about the circumference of the T-section rim of a crank by means of gravity.

Another object of this invention is to provide an improved arcuate disc type crank member ar- A practical embodiment illustrating the principles of this invention is shown in the accompanying drawings wherein: I

Fig. 1 is an elevational view of the crank'and counterweight assembly embodying the preferred construction in accordance with my invention.

Fig. 2 is a cross-sectional view of the assembly taken on the line 2-2 of Fig. 1.

Fig. 3 is a cross-sectional view of a portion of the assembly taken through the clamping pads on the line 3,3of Fig. 1.

Fig. 4 is a cross-sectional view of one of the counterweights only taken on the line 2-2 of Fig. 1.

Fig. 5 is a cross-sectional view of a portion of one of the counterweights only taken on the line 33 of Fig. 1.

Fig. 6 is a cross-sectional view through a portion of one of the counterweights taken on the linefi-Ii of Figs. 4 and 5.

Fig. '7 is an enlarged elevational view of one of the counterweights hanging freely in its unelamped position with its supporting pads in contact with the crank rim.

Fig. 8 is a diagrammatic representation of a force diagram showing the forces exerted on the crank rim by the center clamping member on one side of the rim and the clamping pads on the opposite side of the rim and is a view looking in the direction of the arrows 88 of Fig. 1.

Fig. 9 is a force diagram, shown as an exploded partial sectional view of the elements making up the assembled unit, wherein the various forces acting upon the individual elements effected by the center clamp only are graphically and analytically depicted. Fig. 10 is a diagrammatic representation of the counterweight and rim during a weight adjusting period.

Referring to the drawings the numeral I0 represents a crank shaft forming a part of a reduction gear or other means (not shown) common to the oil field pumping art. M invention may be used with either a single or double pitman and crank structure.

The crank member I I comprises a crank arm I2 and a partial circular disc I3 formed integral therewith. The crank arm i2 is provided with a split head It which connects with the transverse opening I5 adapted to receive the free end of the crankshaft I 0. The extended portions of the split head I4 of the crank arm I2 are drawn together by the clamping bolts I6, thereby locking the arm I2 to the shaft I9. A key H is further provided to prevent relative movement between the crank arm I2 and the shaft I0. The partial circular disc I3 is preferably dis.-

posed eccentrically with respect to the crankshaft opening I in the crank arm I2 but it may be concentric therewith without departing from the spirit of the invention. The portion of the disc I 3 adjacent the crank head I4 is cut away primarily to allow the counterweights I8 to be mounted upon the disc like structure and further to eliminate unnecessary weight of the crank memher I I. The perimetral edge of the disc I3 is T-shaped, having flanges I9, which extend on each side thereof, while the ends terminate on each side of the split head It. Transverse openings are formed through the disc I3 below the T-shaped flanges I9 and adjacent the ends thereof to receive stop plates 28 inserted partially through these openings. These plates are held in place by bolts 2I which pass through openings in the edges of the disc and screw into tapped holes centrally disposed in the plates 20. The function of these stop plates is to keep the counterweights I8 from accidentally slipping off the ends of the discs I3.

: It is preferable to provide each crank member I I with two or more duplicate counterweights I8. Each counterweight is a one piece unitary member in the form of a segment of a sector and has an inverted T-shaped slot forming grooves 22 in the arcuate concave edge, which slot is complementary to the T-shaped perimeter I 9 of the disc I3. When the stop plate is removed from the disc 13 the grooved counterweight may be freely positioned over the flanges I9 of the T-shaped perimeter of the disc, thereby pendulously supporting the entire weight of the counterweight from the periphery of the disc while at the same time the weight is freely slidable relative to the disc I3 between the stop plates 20. The groove 22 in the counterweight I8 is of such proportions as to fit the T-Shaped rim of the crank so that there will be only enough clearance between these surfaces to permit the weight to slide freely on the rim.

In order to be assured that the counterweights will hang plumb on the crank rim, the intermediate portion ofthe undersurface of the inturned flanges or lips 23 of the counterweight I8 is recessed as at .24, thereby providing bearing surfaces or supporting pads 25 at each end of the lips 23. When the weight hangs in a vertical position and loose on the crank rim, the pads 25 of the counterweight will make contact with the rim at the points marked A (see Figs. 7 and 10) and be maintained in a vertical plane. If the weight I8 is above the disc I3 the'bottom 26 of the groove 22, which is oppositely disposed to the surfaces i 24f and .25, will provide the contact surface to engage the rim of the disc and thus support the counterweight on the top of the T-shaped perimeter of the disc.

The counterweight is securely clamped to the T-shaped rim of the crank by means of a plurality of studs and clamping members in a manner to be presently described. A plurality of stud holes 28, normal to the outer surfaces 29 and 30 of. the counterweights, extend through the counterweights at a point such that one edge of the stud holes is substantially tangent to and parallel with the bottom surface 26 ofthe groove 22 while the emainder of said stud holes is entire'lyrwithin the body of the counterweight I8. An aperture or pocket 3|, in registry with the stud holes 28, is provided in the outer surface 30 of the counterweight to receive a block or clamping member 32, which is tapped as at 33 to receive a self locking stud. The tapped hole in the block 4 32 is nearer the end of the block that engages the T-shaped rim section than the opposite end, thus forming a simple lever with a mechanical advantage cf approximately two to one. The inner surface 29 of the counterweight I8 is counterbored as at 34 in registry with the stud holesi28 to receive an elastic stop nut on the free endof the studs. It will be noted from the drawings that the inside surface 35 of the aperture or pocket ill in the counterweight I8 extends inwardly beyond the corresponding edge of the groove 22 for a major portion of its length and at a point indicated at Fig. 6, taken on the line 66 of Figures 4 and 5, a convex abutting surface 36 is provided on this surface which will be vertically in line with the T-shaped rim when the component parts are assembled so that each clamping member 32 will have a substantially full bearing surface against the rim of the crank and at the same time effectively contact the counterweight I8 to form a secure locking means. In the construction disclosed I have chosen to provide the counterweights I8 with three equidistantly spaced clamping members 32 with one stud for each member, the stud for the center member being indicated at 3?, while the studs for each of the two end members 32 are indicated at 38 and the elasti stop nuts as 39.

To be certain that the counterweight will remain plumb while being tightened, a three point bearing against the faces of the crank rim functions in the following manner. The center stud 31 is tightened which produces a reaction between the crank rim I3 and the clamping member 32 of say 10,000 lbs. on one face of the rim. Clamping pads 21, which bear on the face of the rim opposite the clamping members 32, are pro.- vided at the ends'of the weights normal to the supporting pads 25 and in the same radial plane with the supporting pads. A clearance space or recess 21a is provided intermediate the clamping pads to insure a good bearing at the pads only and eliminate any accidental contact with the rim and weight at other points due to imperfections in the castings. The bearing of the face of the rim on the clamping pads provide a reaction of 5000 lbs. each. This reaction is diagrammatically shown in Fig. 8. The two end studs 38 may next be tightened, which will give 2.

an additional clamping action between the weight and the crank'rim.

The method of clamping disclosed in this invention produces compression in the crank rim I3 and a frictional resistance between the crank rim and the weight I8 but does not in any man: ner put any stress on the lips 23 of the counterweight, thereby eliminating any tendency of breaking off a portion of these lips and destroying their guiding feature. The clamping pads 21 act as the fixed jaws of the clamping unit and the clamping member 32 is the movable jaw. The clamping member 32 is so made that the reaction between the clamp and the crank rim is approximately two thirds of the stud pull. For example, assume that the total stud pull is 15,000 pounds and the reaction between the crank rim and clamp is 10,000 pounds. This same stud pull of 15,000 pounds produces a force of 5000 pounds between the clamp 32 and the counterweight I8 at the surface 36 and an additional force of 10,000 pounds between the counterweight and the crank rim. These forces of 5,000 pounds between the clamp and the counterweight and-the 10,000 pounds between the counterweight and the crank rim will produce sufficient frictional resistance to overcome any tendency for the Weights to be thrown off the crank regardless of whether or not the lips 23 of the counterweight are in contact with the crank rim. As mentioned above the lips in no way effect the clamping means in the present disclosure. With this improved construction the only function of the lips 23 is to guide the weight while sliding during adjustment and to keep the weight from falling off the crank when the clamps are loosened. The forces mentioned above are for example only and may vary in the actual practice. Exploded Figure 9 graphically depicts the distribution of forces described above.

The construction disclosed in this invention also provides for easy adjustment of the counterweight. Where it is desirous to move the counterweight circumferentially to a new position, it is merely necessary to determine the position to which it is desirous to move the Weight, by referring to the indexed markings 40 on the face of the T-shaped rim l3, and then rotate the crank rim so that the indicated position forms a vertical center line with the crank and then hold the crank in that position by applying the brake. Next loosen the two end studs 38, leaving the center stud 31 tight which will be sufilcient to hold the counterweight l8 durin the adjusting period (see Fig. 10). At this time apply a wrench (not shown) to the center stud 31 and by tapping the wrench it will be possible to loosen the center stud 31 just enough to allow the weight [8 to slide circumferentially in the groove to the desired position due to its own weight. If the weight, in its loosened condition, tends to twist in a vertical plane on the rim, instead of sliding down the rim by gravity, this twisting is limited by the bottom surface 26 of the groove 22 coming in contact with the outer surface of the crank rim l3 as shown at B in Fig. 10.

Here again it is demonstrated that there is no contact between the clamping mechanism and the lips 23 on the counterweight as is present in some counterweights now on the market. When the counterweight is in its new adjusted position and hanging plumb, tighten the center stud 31 and the two end studs 38 and the mechanism is again ready for service. To facilitate hoisting and placing the counterweight I8 in position on the T- shaped rim I3 a. hole 4| is provided in the counterweight at approximately its center of gravity.

While only the preferred construction according to my invention has been disclosed and described in the foregoing specification it is obvi ous that many changes may be made in the detailed construction thereof without departing from the spirit of the invention and I do not wish to be limited to the exact disclosure set forth but wish to reserve to myself any further embodiments, modifications and variations that may appear to those skilled in the art or come within the scope of the appended claims.

Havin fully described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. A counterweight for use on a crank disc having a T-shaped rim and mounted on a shaft of an oil well pumping apparatus comprising, a unitary weight member having inturned flanges arranged to fit over said T-shaped rim to slidably support said weight member, a plurality of transverse bores through said weight member having their inner surface substantially tangent to the periphery of said rim, pockets in one face of said weight member in registry with said bores and extending inwardly from the face of said member to a surface beyond the corresponding face of said rim, a convex abutment on the inwardly extending surface, clamping blocks insertable into said pockets and contacting said abutments and said rim, and compressive means extending through said bores and engaging said blocks to secure said T-shaped rim, weight member and blocks together as a unitary structure.

2. The apparatus according to claim 1 wherein the distance from the center of the compressive means to the abutment is substantially twice the distance from the compressive means to the rim.

STANLEY S. SHOUP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,221,428 Mahan et a1 Nov. 12, 194.0 2,441,255 Ash-ton May 11, 1948 

